In detecting electric current through weakly conducting liquids, a magnetic compass is often preferred over a standard bulb tester because:

Correct Option

The correct option is

The magnetic tester can detect currents that are too weak to make a bulb glow.

Explanation

Electric current produces different effects, including heating, magnetic, and chemical effects. The choice of an instrument to detect current depends on the magnitude of the current and the sensitivity of the effect utilized by the instrument.

Detailed Analysis:

• Heating Effect (Standard Bulb): A standard bulb tester operates on the heating effect of electric current. For the bulb to glow, the current flowing through the filament must be strong enough to heat it to a high temperature (incandescence). In weakly conducting liquids (such as vinegar or tap water), the resistance is high, resulting in a current that is often too weak to heat the filament sufficiently. Consequently, the bulb does not glow even though current is flowing.
• Magnetic Effect (Compass Tester): A magnetic tester utilizes the magnetic effect of electric current. When current flows through a wire, it generates a magnetic field around it. This magnetic field exerts a force on a magnetic compass needle placed nearby, causing it to deflect. This deflection is observable even with very small magnitudes of current. Therefore, a magnetic compass is a much more sensitive detector for weak currents compared to a heating element.

Key Takeaway:
The magnetic effect of electric current is highly sensitive and can detect weak currents that are insufficient to produce the heating effect required for an incandescent bulb to glow.